fix passing CA files into builtins:fetchurl sandbox (backport #11610)

[mergify[bot]]

Motivation

Context

CA as in Certificate Authority

Priorities and Process

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This is an automatic backport of pull request #11610 done by [Mergify](https://mergify.com).

[mergify[bot]]

Cherry-pick of c1ecf0bee973e620c9282bd71ddf1a5710968249 has failed:

On branch mergify/bp/2.18-maintenance/pr-11610
Your branch is up to date with 'origin/2.18-maintenance'.

You are currently cherry-picking commit c1ecf0bee.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Unmerged paths:
  (use "git add/rm <file>..." as appropriate to mark resolution)
	both modified:   src/libstore/build/local-derivation-goal.cc
	both modified:   src/libstore/builtins.hh
	both modified:   src/libstore/builtins/fetchurl.cc
	deleted by us:   tests/nixos/fetchurl.nix

no changes added to commit (use "git add" and/or "git commit -a")

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[roberth]

• #11686